A major hypothesis in chemical carcinogenesis is that an interaction between the chemical and cellular is a prerequisite for transformation. Cells generally possess DNA repair pathways for at least some of the resulting damage. The absence or deficiency of a repair process may predispose to cancer. This research will investigate the repair of two types of DNA damage, that induced by either benzo(a)-pyrene or methylnitrosourea; in the latter case, repair of a specific lesion, 0/6-methylguanine. Previous experiments with hamster tracheal epithelial cells suggest that benzo(a)pyrene adducts in DNA are repaired by a pathway that differs from ultraviolet light-induced pyrimidine dimers. This will be confirmed by purification of the enzymes involved. Furthermore, DNA repair-deficient cells will be isolated and used both for comparison of the different repair mechanisms, as well as for experiments to isolate the repair genes. With regard to repair of 0/6-methylguanine, we have already transfected DNA from human liver into repair-deficient Chinese hamster ovary cells and selected a clone that expresses the methyltransferase gene. The gene will now be isolated from these cells and used to obtain information on the mRNA and protein structure. Antibodies to the protein, will be obtained using, as immunogen, either the purified protein or a synthetic polypeptide, the sequence of which can be obtained directly from the DNA sequence. The antibodies and genetic probes will be used to assess variations within the human population.